Big bore stroker problems.
The 62mm 60.8 (3mm crank) engine I built back in the summer of 2012 runs good but doesn't like constant high rpm. It pulls off the line great climbs hills without bogging down but has a vibration all the time. I know the bigger bore and stroke will cause the vibration, but after a long full speed run it feels like it has a lot of back pressure. I am running the fmf universal muffler that is for two strokes with the stock head pipe on the cylinder to a custom home made header pipe to add 8 inches to the header pipe to reduce some of the crazy loud noise. I made it curve to the right then back to the muffler like the hammer head exhaust I had seen. It works great on my 155 buggy and the 183cc buggy also just wondering if I should make a larger inside diameter header pipe to get more exhaust out faster.
The stock pipe I/d is about 18.5mm and the head port is 22.5mm. I am thinking of making a larger head pipe out of a Honda seat frame tubing I got from a body shop car. The tubing is mandrel bent already and free!.
The other issue with the performance is the timing chain is advanced due to the cylinder spacer rising the head up about 2mm causing the cam to rotate forward a bit. I had to take off .015 of a inch off the head to get the cam to lay in the head without stretching the chain. I used 400 grit wet paper on the granite counter top for about 2 1/2 hours to get it the head clearance since nobody local wanted to mill my cylinder head. I rotated the head while sanding it in figure 8s and measuring from time to time. I finished it with 600 grit for a nice finish.
I might go to heavier rollers to get the rpms down at cruise. I am running the motorio dr2 with 18mm rollers 10.5/ 12.5. It takes off like a monster but revs out too fast. Next trip to the desert I am going to try 11/13 rollers to get some of the rpm down or 12/14. The motor 183cc will tach out at 7700rpm and my 155cc goes to 8800rpm and is tapped out.
Just want to know if anybody has any ideas for the 183 buggy. The muffler did help on the heat issue and the clattering sound while going in loose sand washes for extended time.
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